1. Field of the Invention
The present invention relates to the automated extraction and purification of a sample using optical tweezers. In particular, the present invention relates to the automated extraction and purification of sperm from samples—particularly sexual assault forensic samples (i.e., swabs, fabric, etc.) using holographic optical trapping.
2. Description of the Related Art
Forensic testing requires critical care for maintaining the chain of custody. Moreover, in areas such as forensic DNA testing, proper handling of the evidence can prevent contamination of the DNA sample, allowing effective PCR (polymerase chain reaction) amplification of DNA from isolated cells and STR (short tandem repeats) analysis.
Because of the nature of the sample collection in cases of rape, for example, separation of the victim's DNA from the perpetrator's DNA is essential for performing a test. Epithelial cells from the victim contain DNA that frequently mix with the DNA inside the sperm of the perpetrator upon testing, confusing the results. Currently, the present technique for separating sperm from epithelial cells, which is widely used, is a sequence of washing steps designed to selectively break open the membranes of one or the other cell type, then washing out of the DNA from that cell type, and then lysing of the second cell type and collection of the second DNA sample. Due to the imprecision of this technique and the variability in the cells and the cell/sample histories, this lysing/washing technique frequently gives STR results with signatures of both the victim and assailant mixed. If the assailant is unknown, a DNA/STR database is used to locate/identify the assailant. For these cases, the mixed STR signatures prevent the use of the database and linking of the forensic data to (a) other crimes, and (b) a possible assailant.
Accordingly, a method and apparatus which would enable three-dimensional manipulation of large numbers of objects with great precision, which could move the objects, such as cells, over large distances, or rotate the objects for analysis from multiple angles, is desired. It would also be desirable to keep a visual record of the processing of the sample, such as by taking images and/or video. It would also be advantageous to have a method and apparatus which could perform this manipulation in sealed chambers, for example, providing no possibility for cross-contamination, and without causing damage to the objects. Further, it would be of benefit to preserve all the materials collected, for storage and potentially further analysis at a later time.